Fibrodysplasia Ossificans Progressiva (FOP)

Written by Professor J M Connor MD, DSc, FRCP for the Muscular Dystrophy Campaign.

Fibrodysplasia ossificans progressiva, also known as myositis ossificans progressiva or MOP, is a disabling condition, which is caused by the formation of bony bars within the muscles of the body. This bone formation is usually first noticed in early childhood as a series of hard lumps in the neck or along the spine. These lumps, which may be tender, gradually shrink in size as the affected muscles are replaced by bone. The appearance of bony lumps in muscles is usually spontaneous but can also be provoked by any injury to the muscles. Disability in FOP is physical and very variable in extent; intelligence in unaffected.

Contents:

• How does the condition progress?
• Can any muscles be affected?
• What is the life-span of people who have FOP?
• Are there any other features of FOP?
• How common is FOP?
• Is FOP hereditary?
• Is there a treatment?
• Does anything make FOP worse?

How does the condition progress?

FOP is progressive in that more muscles become involved with increasing age, but the rate of progression is very variable from one person to another. Furthermore the condition tends to show long periods of inactivity (of up to several years in length).

Can any muscles be affected?

Certain muscles are never involved in this disease. These include the muscles of the eyes, the face, the tongue, the gullet, the intestines and the muscles of continence (bowel and bladder control). The heart is never involved in this condition. Chest expansion may be reduced in FOP but the diaphragm, which is the single most important breathing muscle, is never involved.

What is the life-span of people who have FOP?

General health remains good and several people with FOP in Britain are over 60 years old. In view of the reduced chest expansion respiratory tract infections need to be treated vigorously.

Are there any other features of FOP?

Most people affected by FOP have some abnormalities of the fingers or toes. The big toes are most commonly involved and are usually shortened and deviated. These changes to the big toes are usually apparent at birth.

How common is FOP?

This disorder occurs in all countries in the world and affects about one person in a million. Men and women seem to be equally affected.

Is FOP hereditary?

The basic genetic error is a mutation in the activin receptor IA (ACVR1) gene. In most affected patients worldwide an identical mutation is found and this mutation is not present in the parents and has occurred at the moment of conception. In this situation the chances of recurrence in the family are negligible. For a person with FOP, however, there will be a one in two chance of handing on the condition to any children. Further information on this point may be obtained from your local genetic counselling clinic.

Is there a treatment?

Many types of treatment have been tried in the past and none of these has been shown to be of benefit. A number of new medications are being evaluated at the present time and further information about these trials is available on the IFOPA website, see below.

Does anything make FOP worse?

Injury to the muscles can often provoke local bone formation. For this reason intramuscular injections should be avoided if possible. Similarly operations on the muscles to remove pieces of bone almost invariably result in increased bone formation. Also, some forms of dental treatment may result in bone formation in the jaw muscles and you should therefore warn your dentist that you have FOP.




For more information visit the International Fibrodysplasia Ossificans Progressiva Association (IFOPA) website: www.ifopa.org